“Super-slugs” are invading British gardens – and we don’t know how to stop them

Mmmmmm, slimy. Image: Xauxa Håkan Svensson.

The Daily Mail calls it a “slime wave”. The Sun calls them “an army”. Either way, both papers have reported 500bn slugs are set to invade British gardens, after a mild winter created perfect breeding conditions. The Conversation

So is the UK really about to be overwhelmed by slimy slugs? The simple answer is no, but there could be something far worse in store.

Headline numbers alone aren’t necessarily something to get in a lather over. A typical garden can contain several thousand slugs, and the “500bn” figure is derived from estimates of maximum numbers per area. In any case, slug numbers can rise and fall a great deal across time and space, in natural cycles, and even astonishingly dramatic increases are not always cause for concern. Like waves crashing against a beach, the rise is often transient and local – usually slug numbers will drop back to normal, with the disturbance hardly noticed beyond a few local gardeners.

What is more problematic is the progressive, sustained and perhaps less spectacular rise in numbers which, tsunami-like, is maintained for far longer, and spreads widely throughout the countryside. This is Britain’s real slug invasion. So what can we do about it?

The trigger seems innocuous enough in isolation: a few non-native slugs from continental Europe have accidentally been introduced. Several of these species have close relatives in the UK, so similar in fact that only specialists can tell them apart, and they can interbreed freely. Of course, many animals can create hybrids without presenting a threat, but what makes slugs different – and these hybrids so worrying – is their interesting and deviant sex lives.

This is a hybrid between a ‘Spanish stealth slug’ and the UK’s common black slug. Image: Les Noble/author provided.

Slugs are hermaphrodites, which means the same individual exists as both sexes; they first develop as males, before experiencing a true hermaphrodite phase to become female. This means they can dispense with normal mating requirements, and this is where the consequences of the difference between British and continental species becomes significant.

Why British slugs are different

When slugs colonised the UK after the last ice age, they found an island recently covered with ice sheets, where the biological diversity remained poorer than continental Europe. In these circumstances, the ability to self-fertilise was a good evolutionary strategy, one which ensured reproduction even when slug populations were devasated by harsh weather.

A downside of such continued close inbreeding (and mating with oneself is as inbred as it gets) is a rapid loss of genetic variability, and some British slug species eventually came to consist of almost genetically identical individuals. This meant they were more vulnerable to parasites and pathogens that could rapidly evolve to overcome their defences.

Meanwhile, in continental Europe, slugs were becoming more diverse, as balmier weather meant parasites and pathogens were a bigger issue than finding a mate. These slugs tended not to self-fertilise, and were genetically highly variable. This made at least some of them more resilient to attacks from parasites – a possibility not afforded to the inbred British slugs.

Echoes of these different past environments resonate in contemporary species. British slugs, adapted to a variable climate and dearth of mates, have fallen into the clichéd “No sex please, we’re British” mould, producing fewer, bigger eggs later in life by self-fertilisation. Continental slugs, meanwhile, adapted to resist rapidly evolving enemies. Their strategy is therefore to produce many smaller eggs earlier in life, which maximises genetic diversity and compensates for losing many individuals to infection.

The ‘Spanish slug’, one of Britain’s key invaders. Image: tviolet/creative commons.

These different adaptations weren’t an issue until humans disturbed the natural order by moving slugs back and forth as stowaways in commercial produce. As a result of this, we’ve seen widespread breeding between British and continental species. These new hybrid “super-slugs” are highly fertile, and their genetically diverse offspring are adapted to cope with both the British climate and parasites and pathogens, most of which remain in continental Europe anyway.


Fighting the slug invasion?

Legislation aimed at environmental protection has led to the EU banning commercial use of molluscicides (pelleted chemicals which poison slugs but cause collateral damage to other wildlife). Instead, the emphasis is on using natural enemies like nematode worms, though these are generally ineffective against the larger invasive hybrids.

Nonetheless, the increased slug biomass could still host important veterinary or agricultural parasites and pathogens, spreading more plant and animal diseases. Remarkably, despite their obvious presence in our gardens, we remain startlingly ignorant of the fundamental biology of slugs; evidenced by recent work which increased the number of identified British species by more than a fifth.

So where are we going with this phenomenon? Studies have already found invasive slugs and snails can destabilise ecosystems and reduce biodiversity in the US and Scandinavia. Something similar is happening here in the UK.

The good news is that our research suggests population sizes do eventually begin to decline, after 30 to 40 years. The ecosystem may eventually rebound from this slug invasion, but it remains to be seen how long it will take and what the lasting effects will be for the spread of diseases, ecosystem services, or British biodiversity.

Leslie Noble is a reader in zoology at the University of Aberdeen.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

This app connects strangers in two cities across the world. But can it tackle urban loneliness?

New Delhi, in India, where many of Duet-App's users come from. Image: Ville Miettinen

“You can be lonely anywhere, but there is a particular flavour to the loneliness that comes from living in a city, surrounded by millions of people”. Olivia Laing, The Lonely City

Our relationship to where we live and the spaces we inhabit define who we are and how we feel. But how often do we articulate the emotional impact of this relationship, whether this be loneliness, frustration or even civic pride?

“When I moved to a new city, started living alone, wanted to drink less, stay indoors more, and when I realised that I cannot make any more best friends.”

A new social network, a simple app that connects two individuals from the UK and India, aims to counter some of these issues.  Over the course of a year connected pairs receive one question a day through the app and their responses are exchanged with each other. A simple interaction that gradually builds a series of one-on-one relationships and invites users to imagine, over time, the other person living their life.

Distant geographies are an implicit part of the experience, therefore many of the questions nudge users to explore correlations between their physical and emotional landscapes. The data shows us that many of the Duet-App users are located in populous urban cities like Delhi, Bangalore, Manchester, Leeds and London, places that can just as often discourage feelings of belonging and place-making as much as they foster them.

“I had thought I'd never be able to live here again. but here I am living again at home after almost a decade living elsewhere. Living in Mumbai is a contact sport, and I can't do without it's chaos and infectious energy.”

Mumbai, India. Image: Deepak Gupta

In general cities are getting bigger and spreading wider at the same time as our communications are increasingly being conducted online and via digital gateways.

There is a sense that much of our online personas project an idealised version of ourselves; we increasingly document and express our daily lives through a filter and we are not always comfortable with a spontaneous expression of ourselves. Duet-App seeks to foster alternative digital relationships that through their anonymity allow us to be more honest and free.

“I feel a lot of people assume that I always have a lot going on for me and everything's always happy and amazing. I wish they could appreciate... how much of my own anxiety I swim in every single day. I appear and behave “normal” on the outside, calm and composed but there are always storms going on in my head.”

In exploring the responses to the questions so far, those that often garner the most replies relate directly to how we feel about our personal position in the world around us. Often these questions act as provocations not only to share responses but to reflect and articulate our thoughts around how we feel about what we are doing in the here and now.

Manchester, another popular city for Duet-App users. Image: Julius 

“Sometimes I feel sad about it [getting old] because I saw how easy it would be to feel lonely, and the fact that the world is set up for able-bodied young people is a bit of a travesty.”

Although many social media platforms allow for distant engagement and access into the lives of others we are in the main still curating and choosing our friendship circles. Through Duet-App this is randomised (and anonymised) with the intention of bypassing the traditional mechanics of how we broker online relationships. While directly exploring the digital space as a place for intimacy.


“Where do you go for peace?

“Well the internet, really. I do some mindless browsing, peek into the fandoms, listen to a few songs. Calms me down.”

Snapshots into the lives of someone existing and playing out their lives remotely can highlight shared concerns that break down preconceptions of how life is lived by others. Prompted by the reflections of a stranger exposed to our lives, digital relationships can encourage us to address the physical space we inhabit and the effects that the cities we live out our lives in have on our own well being. 

Catherine Baxendale is director of Invisible Flock.

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